This invention relates to ionic compounds and methods for their preparation. In particular the invention relates to ionic compounds which are liquid or semi solid at a temperature below 150° C., preferably below 125° C.
There is a lot of interest in the field of ionic liquids in recent years and scientific publication and number of patent applications in this area are growing at very fast pace. Ionic systems, which are examples of viscous molten salts, have a number of interesting and useful properties, and have utility, for example, as highly polar solvents, co-solvents and catalyst in synthetic chemistry. They also have found to be useful in applications in various fields such as electrochemistry, synthesis of chemicals compounds, dyes, batteries, fuel cells, photovoltaic devices, electrodeposition processes, semi conductor cleaning, pyrolysis, gasification, in applications involving cellulose dissolution, for the electroplating of metals as described, for example in U.S. Pat. No. 6,573,405, U.S. Pat. No. 7,183,433, U.S. Pat. No. 7,196,221, US Patent Appl. No. 2005/0147889, U.S. Pat. No. 6,527,977, US Patent Appl. No. 2008/0307703, US Patent Appl. No. 2006/0183654, US Patent Appl. No. 2009/0247432.
Ionic liquids exhibits very low or no vapour pressure and thus, in contrast to many conventional molecular solvents and are produce virtually no vapours. They are therefore advantageous from a health, safety and environmental point of view.
U.S. Pat. No. 4,764,440 discloses low temperature molten compositions, formed by reacting, for example, trimethylphenylammonium chloride with aluminum trichloride. The resulting ionic compound has a low freezing point (around −75° C.), but suffers from the water sensitivity as EMIC-AlCl3, because of the presence of aluminum trichloride.
Other metal halides, in place of aluminum trichloride are reported, for example, U.S. Pat. No. 5,731,101 discloses the use of iron and zinc halides as the anion portion of an ionic liquid composition. The cation portion is formed by an amine hydrohalide salt, of the formula R5N.H.X. This reference indicates however that the aluminum compounds are preferred, and indeed contains comparative examples which indicate that it is not possible to substitute SnCl4 for aluminum trichloride. Furthermore, it does not suggest the use of quaternary ammonium compounds as cations.
In another disclosure, U.S. Pat. No. 5,892,124 liquid salts of the general formula Q+A−, wherein Q+ represents quaternary ammonium or phosphonium, and A− represents a various anions including tetrachloroaluminate, and trichlorozincate are disclosed. Diels-Alder reactions were suggested using the such compounds.
In another relevant disclosure, U.S. Pat. No. 6,573,405, ionic compound formed by the reaction of a quaternary ammonium compound of the formula R1R2R3R4N+X− or a mixture of two or more thereof; with a halide of zinc, tin or iron, or a mixture of two or more thereof are disclosed. Preferably the choline chloride with zinc chloride ionic compound was suggested for applications in electrochemical, electrodeposition, electrochromics and dissolution of metal oxides, battery and Diels-Alder reactions. The examples of the invention teach us in which ionic liquid is prepared from a quaternary ammonium compound (Choline Chloride) and metal halide (zinc chloride) is common except for battery where iron halide was also used.
In yet another relevant disclosure, U.S. Pat. No. 7,183,433, ionic compound formed by the reaction of a quaternary ammonium compound of the formula R1R2R3R4N+X− or a mixture of two or more thereof; with for example with urea.
Similarly, attempts were made to form ionic compounds of quaternary ammonium compound of the formula R1R2R3R4N+X− and with specific hydrogen donors belonging to the families, such as carboxylic acids, amides, ethers, esters, aldehydes, ketones, alcohols, carbohydrates. Anions of quaternary ammonium compound of the formula R1R2R3R4N+X− were chloride, nitrate and tetraborate and examples suggest that few ionic liquids were formed with the hydrogen donors, though many of them did not melt till 150° C. Effect of anion X− was studied with symmetric amine salt by varying the anion. The example in which ionic compound made with urea suggests that asymmetric amine salts are preferred.
In yet another relevant disclosure, U.S. Pat. No. 7,196,221, ionic compound formed by the reaction of a quaternary ammonium compound of the formula R1R2R3R4N+X− or a mixture of two or more thereof; with a hydrated metal salts (chlorides, nitrates, acetates, sulphate salts of) of chromium, calcium, magnesium, cobalt, zinc, copper, lithium, manganese, iron, nickel, cadmium, tin, lead, bismuth, lanthanum, cerium. Ionic liquids of other amine salts, tetraethylammonium chloride, triethylammonium chloride and benzyl trimethylammonium chloride with hydrated chromium chloride were also prepared. The examples teach us ionic compounds prepared in the current disclosure are used in applications of electrochemistry, chemicals synthesis and radical polymerization.
In yet another disclosure US Patent Application No. 2006/0183654, where ionic liquid formed by the reaction of immidazolium, pyridinium, pyrrolidinium, quaternary ammonium and phosphonium compounds with carboxylic acids, amides, sulfates, sulfonates and urea. The invention discloses the use of ionic liquids prepared from immidazolium, pyridinium, pyrrolidinium, quaternary ammonium and phosphonium as cation providing sources with carboxylic acids, amides and urea in semiconductor cleaning processes.
In yet another disclosure US Patent Application No. 2009/0247432, use of ionic liquid formed by the reaction of ammonium compound of the formula R1R2R3R4N+Cl− and ClR1R2R3R4N+Cl− and amides such as urea and carboxylic acids. The disclosure teaches us the use of ionic liquid in dissolving cellulose material from the subterranean region where cellulosic material was used as drilling and fracturing fluid.